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Simple Custom Font Rendering Can Poison ChatGPT, Claude, Gemini, and Other AI Systems

Cybersecuritynews •Guru Baran • March 17, 2026

A novel attack technique that exploits a fundamental blind spot in AI web assistants the gap between what a browser renders for a user and what an AI tool actually reads from the underlying HTML. Using nothing more than a custom font file and basic CSS, attackers can silently deliver malicious instructions to users while […]

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Custom Font Attack Exploits AI Assistants' Blind Spot A new attack technique has been discovered that targets AI web assistants by exploiting the gap between what browsers render and what AI tools read from HTML. Researchers at LayerX demonstrated that custom fonts and CSS can be used to hide malicious commands within seemingly harmless text, effectively tricking AI assistants like ChatGPT, Claude, and Gemini into providing false assurances about the safety of executing these commands. The attack relies on social engineering, where users are lured into executing harmful instructions displayed on a webpage. LayerX reported the vulnerability to affected AI vendors in December 2025, with Microsoft acknowledging the issue and addressing it, while Google later downgraded the severity. The technique has been successful against multiple AI assistants, raising significant concerns about the reliability of AI in assessing webpage safety. The attack method remains a critical security concern as it exploits a fundamental flaw in AI assistant design. 3 sources 65

Extracted Entities

Tools (1)

Custom Font File